The present invention relates to aquaculture and, more particularly, to a method for xe2x80x9coff-the-shelfxe2x80x9d storage of enriched nematodes used in feeding aquaculture organisms such as fish and shrimp larvae.
A major bottleneck to the successful growing of marine fish with commercial potential is the rearing of the early developmental stages or larvae. During this time, mortality can range from about 60-100%, frequently due to insufficient or poor nutrition. For instance, hatcheries depend on the provision of live food or zooplankton to the larvae such as rotifers (Brachionus plicatilis or other Brachianus sp.) and brine shrimp (Artemia sp.). These zooplankters do not represent the natural diet but are relatively easy to grow in large quantities and are readily accepted by the larvae. On the other hand, the culture of these zooplankters requires a considerable investment in infrastructure (tanks, water and air pumps, water treatment) as well as energy and manpower. Moreover, the live food cannot be stored or is deficient in specific long chain polyunsaturated fatty acids (PUFA), such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) which are necessary in the diet for rapidly growing larvae which can demonstrate daily a relative growth rate (RGR) of 25-50% (Koven, W., Tandler, A., Kissil, G. Wm., Sklan, D. 1992 The Importance of n-3 highly unsaturated fatty acids for growth in larval Sparus aurata and their effect on survival, lipid composition and size distribution. Aquaculture 104, 91-104). This is also true with arachidonic acid (ArA) which has recently been recognized as playing a central role in increasing stress resistance (Koven, W., Barr, Y., Lutzky, S., Ben-Atia. I., Weiss, R., Harel, M., Behrens, P., Tandler, A. 2001. The effect of arachidonic acid (20:4nxe2x88x926) on growth, survival and resistance to handling stress in gilthead seabream (Sparus aurata) larvae. Aquaculture 193, 107-122). Consequently, rotifers and Artemia must be enriched with these PUFA, by feeding them commercial DHA and EPA preparations, before they are offered to the fish larvae.
Live food culture systems are frequently plagued by an inconsistent supply of zooplankters that have variable nutritional content and are susceptible to sudden population crashes. So for instance an interruption in the supply and/or an inconsistency in feed quality of food fed to the larvae can severely reduce their growth rate, extending the residence time in the hatchery or resulting in smaller, less robust larvae being transferred to the nursery, resulting in reduced growth and survival. In addition, poor feeding can cause stress, resulting in a decreased resistance to disease. In recent years, primarily due to over exploitation, there has been a rapid decline in the world wide availability of Artemia cysts resulting in fluctuating prices and reduced cyst quality compounding the problems of providing these zooplankters.
A clear advantage in the use of nematodes as a feed is in that the nematodes can be stored in a dormant-desiccated state, after enrichment. They can be encapsulated and revived at a later stage for feeding to larvae. This xe2x80x9coff the shelf conveniencexe2x80x9d provides a dependable and nutritionally consistent food supply to the larvae that can be provided, with less investment, than other conventional live food species.
Essential fatty acids for marine larvae such as docosahexaenoic acid (22:6nxe2x88x923), eicosapentaenoic acid (20:5nxe2x88x923) and arachidonic acid (20:4nxe2x88x926) can be provided to the nematodes through various oil emulsions. Previous studies have shown that nematodes readily filter the micelles of oil emulsions. Recent studies have shown that the use of liposomes to feed nematodes is a promising approach to widen the range of feeding additives that could be used for enrichment. Liposomes are small (0.025-1 xcexcm) lipid vesicles consisting of an aqueous volume surrounded by a bi-lamellar phospholipid membrane. It is relatively easy to incorporate water-soluble vitamins, minerals, proteins and amino acids into the aqueous volume and/or lipid-soluble nutrients such as lipids, vitamins and pigments into the liposome""s phospholipid membrane (Koven, W., Barr, Y., Hadas, E., Ben-Atia, I., Chen, Y., Weiss, R., Tandler, A. 1999. The potential of liposomes as a nutrient supplement in first-feeding marine fish larvae. Aquaculture Nutrition 5, 251-256).
A recent study showed that liposomes could be used to enrich Artemia nauplii with the free amino acid methionine (Tonheim, S.K., Koven, B, Rxc3x8nnestad, I. 2000. Enrichment of Artemia with free methionine. Aquaculture 190, 223-235). This zooplankter is generally deficient in this amino acid and its enrichment may contribute to more efficient protein synthesis. This approach has recently been expanded to include the enrichment of nematodes with this and other free amino acids as well as free fatty acids, which stimulate digestive hormones in the larvae such as cholecystokinin (CCK). CCK is a major factor in the release of pancreatic enzymes resulting in enhanced digestion and assimilation of dietary nutrients. In addition, liposomes fed to nematodes containing immunostimulants, vaccines and other pharmaceuticals may stimulate disease and stress resistance in the larvae resulting in improved larval and juvenile fish quality.
U.S. Pat. No. 5,183,950 to Popiel et al teaches a method for commercial storage and shipment of entemogenous (parasitic to insects) nematodes. It relates to methods to desiccate, package, store, and ship insect parasitic nematodes in both large and small quantities while maintaining their viability and pathogenicity to insects. Popiel""s method does not mention enriching the nematodes before storage.
U.S. Pat. No. 5,042,427 to Bedding describes a method of storing and transporting nematodes by using clay to dry the nematodes, which are revived when dispersed in water. Bedding""s method does not mention enriching the nematodes before storage.
Desiccation of nematodes is also taught by Solomon et al. (Solomon A., Paperna I., Glazer I. 1999 Desiccation survival of the entomopathogenic nematode Steinernema feltiae: induction of anhydrobiosis Nematology 1 (1), 61-68) as well as by Perry (Perry R. 1999 Desiccation survival of parasitic nematodes. Parasitology 119,S19-S30). Here again there is no mention of enriching the nematodes before desiccation.
WWO Pat. No. 95/18527 to Agricultural Genetics Company LTD teaches enriching nematodes with various additives such as various oils and pigments for use as live feed for larvae. This method illustrates the advantages of feeding enriched nematodes to larvae but there is no mention of long term storage of the nematodes.
There is thus a widely recognized need for, and it would be highly advantageous to have, a process for preserving and storing nematodes having an increased feeding value devoid of the above limitations.
According to one aspect of the present invention there is provided a process for preserving nematodes having an increased feeding value. The process comprises the steps of enriching nematodes with aquaculture feed additives and desiccating enriched nematodes.
According to another aspect of the present invention there is provided an improved method of aquaculture. The method comprises the steps of enriching nematodes with aquaculture feed additives, desiccating enriched nematodes, storing the desiccated enriched nematodes, rehydrating and reviving the desiccated enriched nematodes; and feeding rehydrated enriched nematodes to an organism being grown in the aquaculture.
According to another aspect of the present invention there is provided an improved method of aquaculture. The method comprises the steps of desiccating nematodes, storing the desiccated nematodes, rehydrating and reviving the desiccated nematodes, enriching nematodes with aquaculture feed additives and feeding rehydrated enriched nematodes to an organism being grown in the aquaculture.
According to further features in preferred embodiments of the invention described below, the process further comprises the step of culturing nematodes.
According to still further features in the described preferred embodiments, the process further comprises the step of storing the desiccated nematodes.
According to still further features in the described preferred embodiments, the nematodes are free-living nematodes.
According to still further features in the described preferred embodiments, the free-living nematodes are of the species Panagrellus.
According to still further features in the described preferred embodiments, the step of enriching nematodes includes providing at least one enriching additive selected from the group consisting of essential fatty acids, vaccines, hormones, immunostimulants, attractants, nutrients and pigments.
According to still further features in the described preferred embodiments, the step of desiccating the nematodes is performed by inducing one item selected out of the group consisting of quiescent anhydrobiosis and osmobiosis.
According to still further features in the described preferred embodiments, the step of enriching is affected by feeding the nematodes with liposomes containing enriching additives.
Among the advantages of off-the shelf convenience are:
a) The ability to store enriched nematodes ensures constant food supply for the larvae. Due to the rapid daily larval growth rate (RGR of 25-50%), the interruption of food supply, as a result of equipment failure, crashes in rotifer and algal cultures and lower hatching rates in poor quality Artemia cysts, can translate into less than optimal larval growth and survival.
b) As batches of enriched nematodes can be tested for nutrient content before storage, consistent nutritional quality can be ensured before feeding larvae.
c) The ability to produce a product for storage, means that sufficient reserves can be built up. This is advantageous otherwise further investment in infrastructure, labor and energy as compared to any other traditional food supply method will be necessary.
d) The ability to store enriched nematodes is a basis for a commercial product that could compete with Artemia cysts, which is a resource plagued by dwindling supply, variable quality, occasional contamination with pesticides fluctuating high prices, and is a non-sustainable resource.
e) Newly hatched Artemia""s body composition can reflect only natural processes in the environment in which the Artemia broodstock dwelled. Cyst laying, being a natural process, lends NO control over quality of the hatched nauplii, in terms of body composition. On the other hand nematodes, which address the same size larvae, can be enriched prior to their encapsulation for long term storage.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a process for preserving and storing nematodes having an increased nutritional value for later use as needed in the feeding of aquaculture organisms.